This invention pertains to computer based methods for determining whether a frontal or angular collision situation in a vehicle may require activation of a safety device. More specifically, this invention pertains to the placement of acceleration sensors in a vehicle and the continuous selective use of their integrated velocity and displacement signals in frontal and angular collision situations to help to determine whether a safety device, such as a passenger compartment air bag, is to be activated and, if so, how it is to be activated.
Safety devices for the protection of the operator and passengers of automotive vehicles have been in use for many years. Many safety features function in a collision situation without external activation. Seat reinforcement, seat headrests, and passenger compartment padding are examples of such safety items. Other safety devices such as supplemental inflatable restraints, popularly known as air bags, require external activation when a collision event is apparently occurring.
Air bags comprise an inflatable bag, an electrically actuated igniter and a gas generator. Each bag is folded and stored with its igniter and gas generator in vehicle locations, such as, the steering wheel pad, instrument panel, door panel or body pillar. Air bags also require a collision detection system that determines when the bags should be deployed and signals the ignition of one or more charges (or stages) of the gas generator. Some passive passenger protection systems, rely on acceleration sensors (detecting abrupt vehicle deceleration) and a micro-processor based controller. An acceleration sensor is a device that continually senses accelerative forces and converts them to electrical signals. The controller continually receives acceleration signals from each sensor and processes them to determine whether a collision situation is occurring that requires air bag deployment.
The content of such a collision detection system for safety device actuation usually depends upon the method or algorithm used by the controller for assessing collision severity. Most systems rely on an acceleration sensor placed in the passenger compartment, close to the center of gravity of the vehicle. This sensor is often put under the passenger seat as part of a sensing and diagnostic module (SDM) of the vehicle collision sensing system. In addition, some systems place one or more accelerometers at the center or sides of the radiator cross-tie-bar (called electrical frontal sensors, EFS) to detect vehicle front-end deceleration indicative of a collision. The collision detection controller receives signals from the acceleration sensor(s) and evaluates them in a pre-programmed manner to determine whether air bag deployment is necessary. The program may also determine the degree of deployment, e.g., one or two inflation stages, of the bag.
The algorithms of collision sensing controllers have involved differing degrees of complexity. For example, acceleration values from a single sensor (e.g., the SDM sensor) have been compared with a pre-determined threshold acceleration value as a test for device deployment. Values from more than one sensor location have been used in the collision sensing practices. Acceleration values have been integrated over time to yield crush velocities, and further integrated to yield crush displacement values. Further, the derivative of acceleration values have been determined as xe2x80x9cjerkxe2x80x9d values. Such velocity and displacement values, and jerk values, have also been compared with respective pre-determined threshold values as a more selective basis for achieving timely air bag deployment. Also, acceleration data has been used in combination with seat occupancy information and seat belt usage to determine air bag deployment.
There are variants in vehicle front-end collision modes and, of course, there can be considerable variation in the severity of a collision depending upon the relative structure and mass of the vehicle and its collision object as well as the relative velocities at the onset of a collision. With respect to front-end collision modes, a vehicle may collision head-on with another vehicle or fixed object in a frontal collision mode. Front-end collisions of a vehicle with other vehicles often occur in an angular mode between head-on (zero degree) and a side-ways collision (ninety degrees). A further distinction is often made between an angular collision with a rigid or non-yielding object and an offset deformable barrier (ODB mode). Exemplary vehicular collision testing reveals different patterns of front end and passenger compartment crush velocities and displacements associated with different collision modes. In fact, considerable collision testing of a vehicle has been required to provide the substantial database of threshold values of jerk, acceleration, velocity and/or displacement over a collision period for use by a collision sensing controller. Such data must be compiled from suitably instrumented test vehicles over the relevant duration of each test collision period. Depending upon the nature and severity of a collision, an airbag deployment decision may be made by the controller process at any time during a period of from about 15 milliseconds (ms) to 70 ms or so from the onset of the collision.
It would be desirable to further calibrate the control systems for airbags and other such devices. It is common practice in calibrating such control systems to develop the required calibration data from measurements taken in exemplary collision testing of each new vehicle model so that the control system calibration for that model is established according to its collision characteristics. It would be desirable to provide a calibration method which does not require actual testing of vehicles or reduces the need for testing of vehicles. In the prior art, attempts have been made to discriminate the severity of the collision event using acceleration and jerk signals which are difficult to generate from computer simulations, such as finite element analysis. It would be desirable to obtain a collision sensing system algorithm that relies upon velocity based measures which can be obtained without collision testing prototype vehicles to calibrate the collision sensing system. Preferably, the velocity based measures are obtained by use of computer or finite element models for calibration of collision sensing systems.
Accordingly, it is an object of this invention to provide an alternative method of activating an air bag or other collision-responsive safety device that can utilize only velocity and displacement values obtained from a suitable collision model. It is a further object of this invention to provide an airbag activation method that utilizes a consideration of more than one vehicle collision mode in use of time integrated acceleration sensor data.
This invention provides a vehicle collision sensing system which helps to determine when to actuate a safety device. This is accomplished by use of vehicle mounted accelerometers and an associated signal processing algorithm in a microprocessor. The collision sensing algorithm is composed of parallel assessment-branches or modules for detecting different collision modes, each of which uses only current velocity and displacement measures calculated by integrating the acceleration data recorded from vehicle mounted accelerometers.
In accordance with the invention at least two front end acceleration sensors are employed together with at least one sensor in the passenger compartment. For example, two frontal acceleration sensors (EFS), may be mounted at the left and right sides of the radiator cross-tie-bar in the engine compartment of the vehicle for sensing the acceleration of the tie-bar. The vehicle is also provided with an accelerometer in the passenger compartment, such as a location underneath the passenger seat as a part of a sensing and diagnostic module (SDM) of the vehicle collision sensing system. The vehicle collision sensing system detects and discriminates the severity of the collision incidents by signals derived from the front end (EFS) acceleration sensors and the SDM acceleration sensor. Such derived signals are used in the signal processing algorithm of this invention which is implemented in the control program within the microcomputer of the collision sensing system.
In a preferred embodiment of the invention, the control method uses sensor data in a manner to determine air bag inflation needs in each of a frontal collision mode, an angular collision mode and an ODB collision mode. A different combination of representative collision modes could be used but these three are exemplified. In general, the collisions are classified into different modes based on similar signal patterns. The name one chooses for the modes is indicative of the main type of collisions that fall into that classification, e.g. frontal mode characterizes the events with patterns similar to the full frontal barrier events, angle mode characterizes the events with patterns similar to the angle barrier events, etc. Other type of collisions may have similar patterns with the ones in the modes already chosen, e.g. pole events may behave relatively similar to the ODBs or offset rigid barrier events may behave similar to the full frontal events, and accordingly are classified into those modes.
When activated by a representative acceleration value indicative of a possible collision, the subject method proceeds by integrating acceleration data from each of three sensors to obtain corresponding velocity and displacement values for each sensor location. Thus, the acceleration data recorded at both radiator tie bar sensors (Al and Ar) and SDM (As) are used to calculate Vs, Vlm, Vrm, Ss, Sl, and Sr. Here Vs and Ss denote the velocity and displacement, at SDM, respectively; and Vlm, Vrm, Sl, and Sr denote the maximum velocity and displacement at the left and right front-end accelerometer locations, respectively. These values are selectively used in a series of three parallel collision mode calculations and logical tests, namely a frontal mode module, angle mode module, and ODB (offset deformable barrier) mode module. Preferably, each collision mode module has two sub-modules, i.e. the 1st and 2nd stage airbag deployment modules.
Suitably, the sensing algorithm uses the acceleration signals, As, from the SDM accelerometer to enable (or initiate) operation of the collision sensing method of this invention. The control method determines whether the acceleration, As, at the passenger compartment location is equal to or greater than a predetermined acceleration threshold which, for example, may be set at 2 g""s (g being the acceleration due to gravity). If As is not greater than the enable threshold, the program loops back to monitoring the input. This controller cycle is repeated every millisecond or so. If As is equal to or greater than the threshold, the program advances to the next step, i.e. to initiate the system clock and to calculate the several velocity and displacement measures. The sensing system is reset for minor incidents by a reset module which determines whether the velocity measure, Vs, is equal to or greater than a predetermined threshold. If Vs is not equal to or greater than the reset threshold, the program loops back to monitoring the input. If Vs is greater than the threshold, the program advances to the next step.
Once the collision severity determining method is enabled the velocities and displacements are calculated and entered into the three branching program modules; the frontal mode module, angle mode module and ODB mode module. The module for which the 1st stage thresholds are first exceeded initiates the deployment of the airbag. Then its corresponding 2nd stage sub-module determines the severity of the collision by comparing the measures with another set of thresholds. The other modes are ignored after a first stage deployment decision has been made.
In the frontal mode-first stage assessment, velocity values are used. It has been observed that the velocity measures, Vs, Vlm and Vrm are generally higher for severe frontal full-barrier-like impact events. Accordingly, they are used in the method of this invention to determine whether or not to trigger the deployment of the first stage airbag inflator for this type of impact events. If, and only if, all three velocity measures for an event are equal to or greater than a set of velocity thresholds, predetermined by experiment or calculation for the vehicle, the program will send a triggering signal out to ignite the first stage air bag inflation.
If first stage air bag inflation has been commanded through the frontal mode program module, the frontal modexe2x80x942nd stage determination is made. Again, the velocity measures, Vs, Vlm and Vrm are used here to determine whether or not to trigger the deployment of the second stage airbag inflator for this type of frontal full-barrier-like impact events. However, unlike the first stage, an xe2x80x9corxe2x80x9d logic is used to allow a second stage deployment when either one of Vs or xe2x80x9cVlm and Vrmxe2x80x9d meets the threshold condition.
In parallel with its analysis of the frontal mode-first stage the controller is also analyzing the angle (or angles) collision modexe2x80x941st stage and the ODB collision mode-first stage. As stated, results from any collision mode analysis can trigger first stage air bag inflation.
In the case of the angle collision mode-first stage, it has been found that either the passenger compartment velocity measure, Vs, or the front end displacement measures, Sl and Sr (depending upon which side of the vehicle is impacted) are generally high for severe angle-like impact events. Accordingly, it is preferred to use them in the angle mode to determine whether or not to trigger the deployment of the first stage airbag inflator for this type of impact events. In assessing the second stage of the angle mode a suitably high left front end velocity measure, Vlm, can trigger the second stage airbag inflator. In the alternative, a suitably high velocity value at the right front end sensor, Vrm, in combination with a suitably high SDM displacement, Ss, can trigger second stage deployment for right angle-like collision events.
In the ODB mode-first stage a combination of displacement at the SDM and velocity at the affected side are used in assessing the severity of an ODB collision mode type event. Thus, a combination of Ss and Vlm are used to determine whether to trigger deployment of the first stage inflator for a left side and a combination of Ss and Vrm for a right side event. For an ODB-second stage determination Vs and Sl are used for discriminating left side events and Vs and Sr for right side events.
Thus, this invention provides a collision severity determination method that identifies distinct front end vehicle collision modes and associates with these modes crush velocity and displacement data from selected vehicle body acceleration sensor locations. The collision detection controller continually compares acceleration data with a predetermined threshold value indicative of a collision possibility. The controller then determines current values of crush velocity and displacement at sensor locations at the front of the vehicle body and in the passenger compartment. Suitable selections are made from these values to assess, in parallel, each of at least three collision modes to determine activation of an air bag or other safety device. This practice is readily adaptable to managing two or more levels of device activation.
A critical feature of a collision severity determination method is the availability of suitable threshold velocity and displacement values over a period of up to 100 ms for each acceleration sensor and device activation. These threshold values may be based on physical collision test data for the specific vehicle, or collision model data, or a combination of test data and modeling.